Where should I top my plants?

[BigCube]

is it the 3% or the 6% food grade? Hydrogen peroxide I’m not sure which I should order?

Just regular 3%. I get it from the dollar store

 

[skaterdude]

Lumens isn't the right way to measure light for plants because it's weighted to how the human eye perceives light. It gives more weight to the center of the spectrum which is green. Plants need red / deep red (620 nm - 680 nm) and blue (around 450 nm) most. They can use other colors, but it's not as efficient. The daylight bulbs will have more blue, which is good because blue regulates the height of plants so they grow stockier.

Light is usually measured by the number of photons per second. You need more than 500 umol/m2/sec (micro-moles per square meter per second). The quickest way to measure this is to get a PAR meter. As a proxy for that, you could go by the watts of electricity. LEDs have a range of efficiency, so it won't be super accurate, and different wavelengths have different energy levels (blue photons take more electricity to produce, while red take less). You should figure to have at least 400W or electricity powering bulbs for about a 2 x 4 ft area, minimum. I've got 3 plants growing in that space right now and they are doing just OK. Growing a little taller than the last batch (with two of the grow lights) so I think they didn't get quite enough early on, but they have some nice buds on them. In a tent, the reflective inner coating will help you by reflecting "waste" light back to the plants.

I put a couple of 5200 lumen (there's the word again, LoL) 4' LED shop lights vertically to supplement the overhead light and get more light below the top canopy as an experiment. There's no control for it, so can't compare with and without.

 

[BigCube]

Lumens isn't the right way to measure light for plants because it's weighted to how the human eye perceives light. It gives more weight to the center of the spectrum which is green. Plants need red / deep red (620 nm - 680 nm) and blue (around 450 nm) most. They can use other colors, but it's not as efficient. The daylight bulbs will have more blue, which is good because blue regulates the height of plants so they grow stockier.

Light is usually measured by the number of photons per second. You need more than 500 umol/m2/sec (micro-moles per square meter per second). The quickest way to measure this is to get a PAR meter. As a proxy for that, you could go by the watts of electricity. LEDs have a range of efficiency, so it won't be super accurate, and different wavelengths have different energy levels (blue photons take more electricity to produce, while red take less). You should figure to have at least 400W or electricity powering bulbs for about a 2 x 4 ft area, minimum. I've got 3 plants growing in that space right now and they are doing just OK. Growing a little taller than the last batch (with two of the grow lights) so I think they didn't get quite enough early on, but they have some nice buds on them. In a tent, the reflective inner coating will help you by reflecting "waste" light back to the plants.

I put a couple of 5200 lumen (there's the word again, LoL) 4' LED shop lights vertically to supplement the overhead light and get more light below the top canopy as an experiment. There's no control for it, so can't compare with and without.

The lumen spectrum and the par spectrum are the same spectrum, just measured differently.

Lumens are a measure of brightness, par derived from ppfd is the actual amount of photo synthetically available radiation.

But to say you cant use lumens to measure light for growing is wrong. True, it doesnt give you par numbers but it gives you lumens. With a bit of math you can calculate par from lumens using your spectrum as a variable. Also lumens and par being the exact same spectrum, more lumens necessarily equals more par.

Just another downfall of burple, is that you need to do the math or buy an expensive par meter to get readings you'll understand.

A good write up, equations, examples, and full explanation can be found here:

Calculate PPFD for Horticulture

AGi32 Calculates Photosynthetic Active Radiation (PAR) for Horticultural Applications Lighting for plants is different from lighting for humans. Light energy for humans is measured in lumens, with light falling onto a surface measured as illu...

support.agi32.com

 

[skaterdude]

The lumen spectrum and the par spectrum are the same spectrum, just measured differently.

Lumens are a measure of brightness, par derived from ppfd is the actual amount of photo synthetically available radiation.

But to say you cant use lumens to measure light for growing is wrong. True, it doesnt give you par numbers but it gives you lumens. With a bit of math you can calculate par from lumens using your spectrum as a variable. Also lumens and par being the exact same spectrum, more lumens necessarily equals more par.

Just another downfall of burple, is that you need to do the math or buy an expensive par meter to get readings you'll understand.

A good write up, equations, examples, and full explanation can be found here:

Calculate PPFD for Horticulture

AGi32 Calculates Photosynthetic Active Radiation (PAR) for Horticultural Applications Lighting for plants is different from lighting for humans. Light energy for humans is measured in lumens, with light falling onto a surface measured as illu...

support.agi32.com

They are only the same spectrum in the sense that you're measuring visible light from 400 - 700 nm. But the fact is that lumens and ppfd are different types of measurements. One is like measuring the amount of water coming out of a faucet. The other is like measuring how much hits a certain area of the sink. The cited article points this out in the first table. You can convert from lumens to PAR, and you can go from illuminance to PPFD. You can't go from lumens to PPFD without knowing more about the setup. Or you can use a PAR meter that measures it directly. I got a used one for $40 a year ago and it's a great tool.

Also pay attention to "However, not all wavelengths have an equal likelihood of being absorbed, as determined by the various plant pigments that might be present." You can get an approximation of the spectrum using the table of sources. But the spectral output of lights, even with the same rating (like 4000K) can be quite different. That's why there's also a CRI rating (color-rendering index) that tells you how accurately colors will appear under that light. CRI isn't relevant to plants, it just points out that you can't go by the color temperature alone.

Check out this article: http://gpnmag.com/wp-content/uploads/16_TechnicallySpeaking_GPN0913 FINAL_0.pdf

I did a lot of research on this topic when I was designing my grow lights. There was one article in particular that provided some great info, but I can't find it right now. It also pointed out how far infrared affects plant growth. And another article gave me the 500 um/sec/m2 (minimum) to 2000 um/sec/m2 (point of diminishing return) range as best for plant growth.

 

[BigCube]

They are only the same spectrum in the sense that you're measuring visible light from 400 - 700 nm. But the fact is that lumens and ppfd are different types of measurements. One is like measuring the amount of water coming out of a faucet. The other is like measuring how much hits a certain area of the sink. The cited article points this out in the first table. You can convert from lumens to PAR, and you can go from illuminance to PPFD. You can't go from lumens to PPFD without knowing more about the setup. Or you can use a PAR meter that measures it directly. I got a used one for $40 a year ago and it's a great tool.

Also pay attention to "However, not all wavelengths have an equal likelihood of being absorbed, as determined by the various plant pigments that might be present." You can get an approximation of the spectrum using the table of sources. But the spectral output of lights, even with the same rating (like 4000K) can be quite different. That's why there's also a CRI rating (color-rendering index) that tells you how accurately colors will appear under that light. CRI isn't relevant to plants, it just points out that you can't go by the color temperature alone.

Check out this article: http://gpnmag.com/wp-content/uploads/16_TechnicallySpeaking_GPN0913 FINAL_0.pdf

I did a lot of research on this topic when I was designing my grow lights. There was one article in particular that provided some great info, but I can't find it right now. It also pointed out how far infrared affects plant growth. And another article gave me the 500 um/sec/m2 (minimum) to 2000 um/sec/m2 (point of diminishing return) range as best for plant growth.

I clearly understand. You've clearly missed the point. Let me try this:

What units do you use to measure your nutrients?

 

[BigCube]

You're fine with using ml, cc or oz or whatever when measuring nutrients and water.

Why dont you measure them with umol?

The point is, the average cannabis grower doesnt need to measure par. Lumens will do. Do a little math, get your par numbers if that's what you're after. They are the same thing, just measured differently.

No need to spend hundreds of dollars on a par meter. Your cellphone and a bit of math will do if what you want is par. Lux is fine for the rest of us, they are meaningful numbers that directly relate to the amount of light in an area.

I can understand that if you're building led fixtures and for whatever reason want the par numbers without doing the math, that you would go and buy a par meter.

But I would just save my money and do the math. Or better yet, work in lumens or lux.

 

[skaterdude]

You're fine with using ml, cc or oz or whatever when measuring nutrients and water.

Why dont you measure them with umol?

The point is, the average cannabis grower doesnt need to measure par. Lumens will do. Do a little math, get your par numbers if that's what you're after. They are the same thing, just measured differently.

No need to spend hundreds of dollars on a par meter. Your cellphone and a bit of math will do if what you want is par. Lux is fine for the rest of us, they are meaningful numbers that directly relate to the amount of light in an area.

I can understand that if you're building led fixtures and for whatever reason want the par numbers without doing the math, that you would go and buy a par meter.

But I would just save my money and do the math. Or better yet, work in lumens or lux.

You clearly do not understand, because Table 1 in that article (the link I provided) demonstrates just how far off you can be using lumens. For photosynthesis, the energy the plant gets is directly proportional to the number of photons it absorbs. The same is not true of nutrients. Your lumen values give priority to green over other colors, but green photons are more expensive to produce than red, and less efficient in transferring energy to a plant. In addition, green photons do not have the effect on growth that blue photons do. So it's pretty easy to see why lumens is not the best way to measure light for plant growth potential. Just because it's easy to find, doesn't mean it's a good measure. Sure, PAR meters are relatively expensive. Borrow one, or look on eBay or CL. That's how I got one. I've studied this topic a lot. I know what I'm writing about, and my custom LED lights have been very successful.

Measuring nutrients and water are completely different from measuring light. And when you measure pH, you're measuring umol of hydrogen ions in water, you just don't know it by that name because "pH" is easier to use. I don't understand how unit of measurement of nutrients has anything to do with how you measure light. You can't measure the rate of delivery of nitrogen, for example, because there's no constant delivery system unless you're growing hydroponically, and then you DO measure the concentration of the nutrients in the solution, but for different reasons. One measure of solution concentration, btw, is the molarity, which involves the same "mol" as measuring the number of photons (umol).

 

[skaterdude]

Here's one of the most influential papers (to me) that I found on tests of LED lights on plant growths. The differences in growth and productivity are pretty stark between the different trials and illustrate the importance of the different wavelengths. So far, I have not found data specifically for cannabis. that's important because different plants respond differently.

[PDF] High-power light-emitting diode based facility for plant cultivation | Semantic Scholar

Based on perspectives of the development of semiconductor materials systems for high-power light-emitting diodes (LEDs), an illumination facility for greenhouse plant cultivation was designed with the dominating 640 nm photosynthetically active component delivered by AlGaInP LEDs and...

www.semanticscholar.org

 

[BigCube]

Most of us aren't making our own lights. We are using fixtures we bought. Lumens are all we need.
If you're saying the average cannabis grower can't use lumens to get meaningful light readings, you're just wrong.

If that's not what you're saying then I don't care.

 

[LEDNOOB]

So here’s how the two plants I topped are progressing. I will be topping again before flowering so will update again with pics.

 

[BigCube]

Nice, I topped my blueberry kush crosses a few days ago. Ready for scroggin

 

[LEDNOOB]

Nice, I topped my blueberry kush crosses a few days ago. Ready for scroggin

Do you also trim up underneath? I wasn’t sure what else I could get away with snipping... when I put in my scrog shall I trim up underneath then ?